Nanotechnology is believed to have the potential to radically accelerate the prevention, diagnosis and treatment of cancer. As many biologically important processes, including events that lead to cancer, happen at the nanometer scale, it is important to probe the molecular processes and interactions with probes and devices at the nanoscale. The broad objective of this proposal is to develop new multifunctional nanoprobes with superior optical and magnetic properties for enhanced molecular cancer imaging and therapy. These new nanoprobes will not only facilitate multimodality fluorescence and magnetic resonance imaging of cancer, but also will enable magnetic field gradient directed drug targeting and magnetic field guided cancer imaging. The proposed research will focus on the most common cancer afflicting American women - breast cancer, but the nanoprobes and the technologies developed may also be extended for other diseases. The specific aims are: 1) Develop innovative approaches to synthesize fluorescent magnetic nanoprobes with both optimal magnetic and optical properties as compared with commercial and other established magnetic or fluorescent probes. 2) Biologically modify the fluorescent magnetic nanoprobes for specific targeting of human breast cancer cell lines. 3) Design an electro-magnetic device which produces a controllable magnetic field gradient that enables localized targeting and circulation of the fluorescent magnetic nanoprobes for highly effective cancer imaging and therapeutic applications. 4) In vivo evaluation of targeting, imaging and therapy efficacy of HFMN using mouse xenograft model, and demonstrate the enhanced targeting efficacy by external magnetic field gradient control. Achieving these aims will contribute to the discovery of highly effective molecular nanoprobes to promote early detection and treatment of cancer.